Genetically engineered strain wsj-ia for producing isovaleryl spiramycin i

ABSTRACT

A genetically engineered strain WSJ-IA for producing isovaleryl spiramycin I. Also provided is a method for preparing the strain, comprising the steps of: (a) constructing a recombinant plasmid comprising a double gene ist-acyB2; (b) transforming the plasmid into an isovaleryl spiramycin I—producing strain to obtain the strain WSJ-IA. The level of isovaleryl spiramycin I produced by fermentation of the strain WSJ-IA is increased 1.7 times and the fermentation potency thereof increased 4.14 times in comparison with the strain exclusively comprising a single gene ist.

FIELD OF THE TECHNIQUE

This invention comprises acquisition of a bacterial strain producing high content and high yield of a single component antibiotic by constructing with gene regulation technology.

BACKGROUND OF THE INVENTION

Bitespiramycin (primitive name: Shengjimycin) [patent no.: ZL97104440.6] is a derivative of spiramycin formed by isovalerylation of the 4″-position hydroxyl group of the mycarose moiety in spiramycin molecule. It is produced using genetic engineering technology, to generate bacterial genomic combination between the isovaleryl spiramycin gene ist of heat resistant streptomyces and spiramycin. Bitespiramycin has relatively strong activity against Gram-positive bacteria, especially Streptococcus pneumonia, Mycoplasma pneumonia and chlamydia, it exhibits antibacterial activity against erythromycin- and (β-lactam antibiotic-resistant bacteria such as influenza bacillus, Legionella, Clostridium perfringens; it does not exhibit complete cross-resistance with similar drugs. Bitespiramycin has a relatively high lipophicity, its oral absorption is fast with strong permeability into tissues and a wide distribution in the body and a long maintaining time. Therefore it shows a good post-antibiotic effect. Phase III clinical trials for Bitespiramycin produced with genetic engineering technology has been finished, the results showed good therapeutic effect and safety. Application for class I new drug certificate has been put forward for this drug.

Clinic research shows Bitespiramycin is a safe and effective antibiotic. Its therapeutic effect is comparative to antibiotic azithromycin, generally accepted to be the best macrolide currently. Nevertheless, due to the fact that Bitespiramycin is a multi-component drug, for all the efforts to establish tablet production process to be able to obtain products with controllable component proportions and a stable quality, yet the demands on the control of extraction as well as purification processes are relatively rigorous, and the quality inspection process is complex. Meanwhile, to enhance its therapeutic effects, it is necessary to development its injection formulation. It is well known that injections bring about therapeutic effects very quickly, is especially applicable to critically ill patients or those who are not suitable to take the drugs orally. It is certain that injections are more demanding in terms of quality control.

Production of multi-component Bitespiramycin by the corresponding bacteria is stemmed from multi-component characteristics of spiramycin. Being a homogeny of Platenomycin, it is a macrolide antibiotic, its main nucleus being a 16-membered lactone ring. It contains three sugar molecules: forosamine, mycaminose and mycarose, whereas the main component of Bitespiramycin is an isovalerylation derivative of the hydroxyl group in 4″-position of the mycarose moiety in spiramycin molecule. Because the existence of acyltransferase gene in the bacteria producing spiramycin, 3-position of the lactone ring in spiramycin molecule can be acetylated to form spiramycin component II; propionylated to form spiramycin component III; and when the 3-position of the lactone ring is de-acylated, spiramycin component I is formed. Therefore Bitespiramycin is also a mixture of at least three components: isovaleryl spiramycins I, II, III. The structures of three main components of Bitespiramycin are as follows:

wherein:

-   -   Isovaleryl spiramycin III R₁═COCH₂CH₃ R₂═COCH₂CH(CH₃)₂     -   Isovaleryl spiramycin II R₁═COCH₃ R₂═COCH₂CH(CH₃)₂     -   Isovaleryl spiramycin I R₁═H R₂═COCH₂CH(CH₃)₂

Researches showed that single components of isovaleryl spiramycin I, II and III all have antibiotic activities, there are no significant differences in their activities [patent application number: 201010119745.1]. According to present quality standard set for Bitespiramycin, the contents of isovaleryl spiramycins (I+II+III) should be no less than 60%. Therefore, a single component (content higher than 60%) can be used to substitute the multi-component mixture. To reduce the production of multi-components, this laboratory constructed bacterium stain WSJ-2 by blocking the 3-O-acyl transferase gene using gene recombination technology in Bitespiramycin generating bacterium WSJ-1. WSJ-2 produced only the isovaleryl spiramycin I [Chunyan Ma et al. Current Microbiology, 2011, 62:16-20]. However, this strain showed very low fermentation unit, it is thus not conducive to large-scale production. It is the intention of this invention to regulate gene acyB2 to modify WSJ-2 strain, to increase the yield of the single component isovaleryl spiramycin I and its content in the mixture. This will lay the foundation for the development of a new drug: single component of the Bitespiramycin homolog, isovaleryl spiramycin I for clinic use.

It is known that the isovaleryltransferase gene ist from heat-resistant streptomyces is linked with regulatory gene acyB2, the presence of the regulatory gene can activate the expression of ist gene. The model streptomyces strain: Variable Lead Green Streptomyces containing complete ist- as well as acyB2-regulatory genes was able to convert 67-79% of the externally added tylosin to 4″-isovaleryl tylosin, whereas the same strain of Streptomyces containing only ist gene, or ist gene with incomplete acyB2 gene, converted only 0-2.4% of the added tylosin [Arisawa A et al: Biosci Biotechnol Biochem 1993, 57(12): 2020-2025]. By transferring recombinant plasmid of autonomous replication form (vectors pIJ702 or pIJ943) containing ist- and acyB2 genes into tylosin producing bacterium (Streptomyces fradiae), under the condition of external addition of a drug (thiopeptin), the transformant mainly produced tylosin in fermentation, besides a minor amount of 4″-isovaleryltylosin (ca. 56 g/mL)[Arisawa A. et al: J Antibiotics 1996,49(4):349-354] could be detected. However, no reports on the increase of 4″-isovaleryltylosin yield or higher content of single component in the mixture by transferring ist- and acyB genes into tylosin producing bacterium have been published up to now.

acyB2 regulatory gene and the transcriptional regulatory protein Srm28c in the spiramycin producing bacterium (Streptomyces ambofaciens) are homologous [Fatma Karray et al Microbiology 2007,153,4111-4122], their degree of identity is 69%, the degree of identity of acyB2 and regulatory protein tylR in tylosin producing bacterium (Streptomyces fradiae) is 41%, tylR is the positive regulatory protein of the biosynthesis in tylosin producing bacterium, it regulates the expression of a polyketide synthase module (tylGI) in tylosin producing bacterium, and plays a regulatory role on the tylosin glycosyl synthesis as well as the polyketone ring oxidation. High expression of tylR gene in the tylosin producing bacterium can increase the yield of tylosin [George S. et al., Mol. Microbiology 2004,54(5):1326-1334]. However, the method of integration of ist gene into the spiramycin producing bacterium, which is homologous as the acyB2, by means of chromosome-recombinant plasmid homologous DNA recombination technology, only resulted in the production of mixture of isovaleryl spiramycin, with a yield of as high as 800 mg/mL [Shang Guangdong et al. Chinese Journal of Biotechnology, 1999,15(2):171]. This demonstrated that only by transferring ist gene into a strain containing regulatory gene similar with acyB2 would not be able to increase significantly the yield and component content of the target product.

This laboratory demonstrated that by concatenating ist gene using genetic engineering technique, to increase the copy number of ist gene in spiramycin producing bacterium to increase ist gene dosage, the capability of the bacteria to isovalerylate was also increased; it was also demonstrated that by substituting the original ist gene promoter sequence with a promoter with strong activity, such as erythromycin resistance gene ermE promoter sequence, the expression of ist gene could be increased. This increases the production of isovaleryl spiramycin by 62% with the gene engineered bacterium [Patent application No. 200910148767.8 ].

The aim of this invention is to obtain bacterial strains yielding high content of Bitespiramycin single component—isovaleryl spiramycin I, as well as high productivity by means of expression of ist gene linked with regulatory gene acyB2 in a strain, which has already been obtained, capable of producing only the component of isovaleryl spiramycin I, using a highly efficient and stable expression system. To attain this aim, it is necessary to overcome the obstacles of the restriction of the antibiotic producing bacteria of practical value on the gene modification by exogenous gene, thereby improving the conversion rate of the exogenous DNA. Meanwhile, it is necessary to select vector systems for stable express, such that the genetically engineered bacteria can be suitable for large-scale industrial production. This invention proposes to adopt an integrated vector for non-autonomous replication in Streptomyces, such a vector contains the Streptomyces phage integrase enzyme as well as the attachment sites, and contains only the E. coli replicon, to facilitate the preparation in E. coli; meanwhile the vector lacks Streptomyces replicon. When it enters Streptomyces cells, the integration relies on the attachment sites (attP) on the carrier and specific attachment sites of the host bacteria. Therefore, the exogenous gene may be stably expressed in large scale production. The researches on the co-expression of said isovaleryl acylase gene ist and the regulatory gene acyB2 in isovaleryl spiramycin I producing bacterium to increase the yield and content of isovaleryl spiramycin I, as well as the studies on pilot-scale experimental production, have not been found reported to date at home and abroad.

Contents of the Invention

1, This invention provides a strain of genetically engineered bacterium producing high yield and high content of isovaleryl spiramycin I component, said engineered bacterium is a clone strain with isovaleryl transferase gene ist linked with acyB2 regulatory gene co-expressed in isovaleryl spiramycin I producing bacterium WSJ-2.

2, This invention provides the construction of the strain of gene engineered bacterium producing high yield and high content of isovaleryl spiramycin I component, said construction is to use the total DNA of heat-resistant Streptomyces (Streptomyces thermotolarences CGMCC4.1501) as template, design the primers according to the ist-acyB2 sequences announced by NCBI, and to obtain the linked ist-acyB2 gene fragment by means of PCR, insert appropriate cleavage sites; it is also proposed to ligate ist and acyB2 gene fragments, respectively, with the integrative vector transferrable to the isovaleryl spiramycin I producing bacteriuml strain in appropriate cleavage sites, to construct ist-acyB2 gene recombinant plasmid. The ist-acyB2 gene recombinant plasmid is subsequently inserted into isovaleryl spiramycin I producing bacterium WSJ-2, after which PCR is carried out to verify that ist-acyB2 is integrated in the transformant genome to obtain WSJ-IA.

3, This invention proposes to identify the characteristics of the Streptomyces strain WSJ-IA in accordance with the standards of the classification and identification of Streptomyces.

4, Using the isovaleryl spiramycin I producing bacterium WSJ-2 that contains ist monogene as control, this invention tested the fermentation performance of the WSJ-IA strain, including measurement of the fermentation titer of the WSJ-IA strain using microbiological method, and the isovaleryl spiramycin I content in the fermentation broth by means of HPLC quantitative analysis. The results showed that introduction of acyB2 regulatory gene can significantly improve the content as well as the yield of isovaleryl spiramycin I component by the strain.

Effect of this invention: The positive effect of invention is to show that introduction of acyB2 regulatory gene into the isovaleryl spiramycin I producing bacterium' strain WSJ-2 can increase the fermentation titer by 414%, and increase the content of isovaleryl spiramycin component I by 170.2%. The high isovaleryl spiramycin I producing strain constructed in this invention has been pilot tested in a 2 ton fermentation tank, the accumulated isovaleryl spiramycin I samples have been used for pharmacodynamic studies. The application of this strain into the industrial production of this antibiotic component can not only simplify the quality control and testing standard of the product, but also offer conditions for the preparation of the injectable formulation of isovaleryl spiramycin.

THE DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is the construction of ist-acyB2 gene recombinant plasmid pSET52-ia;

FIG. 2 is the PCR result of chromosome of the bacterial strain producing isovaleryl spiramycin and containing ist-acyB2 gene; wherein M: DNA MarkerIII; 1- WSJ-2 control bacterium; 2-5: Transformants WSJ-IA 1-4;

FIG. 3 is the HPLC result of isovaleryl spiramycin component I in the fermentation product by bacterial strain WSJ-IA containing ist-acyB2 gene recombinant plasmid pSET52-ia; wherein A: WSJ-2 control bacterium; B: WSJ-IA, gene engineered bacterium containing ist gene and regulatory gene acyB2; SP-spiramycin; ISO-SP-isovaleryl spiramycin I.

EMBODIMENTS OF THE INVENTION

Following examples only serve to help the technicians of this field to better understand this invention, which are by no means any restriction to this invention.

Example 1 Construction of Recombinant Plasmid pSET52-ia Containing Dual Gene Ist-acyB2

The recombinant plasmid pSW4 constructed previously in this laboratory [Shang Guangdong et al., Chinese Journal of Biotechnology, 1999, 15(2):171] was digested with SmaI-BamHI enzyme to obtain complete ist gene and 1820 segment containing upstream part of acyB2 gene, using total DNA of heat-resistant Streptomyces provided by China General Microbiological Culture Collection Center (Streptomyces thermotolarences CGMCC4.1501) as a template, to design primers according to acyB2 sequence announced by NCBI.

p1: CGCTCAGGGACGCAAGACC and P2: CCGGAATTCGCCCCGTGACCTCACCGTC, PCR temperature: 94° C. predenaturation for 2 min; 94° C. for 30 s, 60° C. for 30 s, 72° C. for 1 min, 28 cycles; extending at 72° C. for 5 min, to obtain 1013 bp segment of the downstream part of acyB2 gene. BamHI-EcoRI enzyme was used to digest the PCR product to obtain 934 bp segment, the aforementioned segments digested by SmaI-BamHI (1820 bp) and BamHI-EcoRI (934 bp) were ligated into in pBluesript II KS(+) vector (E•Merck) by the restriction enzyme sites SmaI-EcoRI, to obtain gene recombinant plasmid pBKS-ia containing ist and complete acyB2. pSET152 plasmid, were ligated into the integrated E. coli/Streptomyces conjugative transfer plasmid via the restriction sites by XbaI-EcoRI enzyme [Bierman M. et al Gene 1992, 116, 43-49, from shared gene bank, www.genecool.com], to obtain ist-acyB2 gene recombinant plasmid pSET52-ia (The experimental method was according to operation procedures, TAKARA Biotechnology (Dalian) Co., Ltd.). Construction process is shown in FIG. 1.

Example 2 Recombinant plasmid pSET52-ia convertion of isovaleryl spiramycin I producing bacterium WSJ-2

Isovaleryl spiramycin I producing bacterium WSJ-2 was constructed by this laboratory [Chunyan Ma et al. Current Microbiology, 2011, 62:16-20]. Said strain was cultured on slant medium [Soybean cake flour 2.0%, glucose 1.0%, starch 3.0%, CaCO₃, 0.5%, NaCl, 0.4%, agar 2.0%] at 28° C. for 7-10 days, to prepare protoplast according to the procedures described in the literature [D. A. Hopwood et al. Genetic manipulation of Streptomyces, A Laboratory Manual, Norwich; John Innes Foundation UK, 1985], Specifically, a piece of strain culture was scooped to inoculate onto R2YE medium containing sucrose, cultured at 28° C. for 2-4 days, the same medium was inoculated by transferring 10% of the above culture with addition of 0.5% glycine, cultured for 20 hours. The mycelium was collected by centrifugation, washed 2-3 times with 10.3% sucrose solution, the mycelium was bacteriolyzed at 37° C. in the P solution containing 2 mg/ml lysozyme for 15-60 min, filter through cotton to obtain protoplasts. To overcome the restriction of the isovaleryl spiramycin I producing bacterium WSJ-2 to exogenous gene modification, first, recombinant plasmids pSET52-ia was transferred to methylation-deficient E. coli 12567 [Mac Neil et al Gene 1992, 111, 61-68, from shared gene bank, www.genecool.com]. Plasmid DNA from the transformant was extracted, subsequently transferred into protoplast under the mediation of PEG, coated on R2YE solid medium. After culture for at 28° C. 24 hours, the culture was covered with solution containing apramycin to attain a final apramycin concentration of 50 μg/ml in the medium, and cultured for 7-10 days, to pick the resistant transformants. The transformants are subcultured continuously without dosing, and then test after dosing to obtain the isovaleryl spiramycin I producing bacterium WSJ-IA with stable expression of resistant recombinant plasmid pSET52-ia.

The primers for upstream of ist gene and downstream of acyB2 gene P3: GAGGTAGAAGGCGAAGGT and P4: CGTCAGATGCCAGTTCAC was designed, PCR was carried out for the total DNA of control bacterium WSJ-2 and transformant (4) of WSJ-IA put forward in the present invention as templates, PCR procedure were: 94° C. predenaturation for 2 min; 94° C. for 30 s, 60° C. for 30 s, 72° C. for 2 min, 28 cycles; 72° C. extension for 5 min (FIG. 2). The obtained results showed that 1733 bp PCR product could be obtained from WSJ-IA genome, whereas no PCR product was obtained from the control strain, this meant that ist-acyB2 gene had been integrated into the genome of the target strain successfully. Said strain has been sent to China General Microbiological Culture Collection Center, No. 1, 3rd Bldg., Beichen West Road, Chaoyang District, Beijing, on Jun. 25, 2010, to be preserved. Accession number: No.CGMCC 3942, category name: Streptomyces spiramyceticus.

Example 3 Identification and Confirmation of the Characteristics of the Strain WSJ-IA

In reference to “classification and identification of actinomycetes” [Yan Xunchu ed., 1992], this invention identified and confirmed the characteristics of the WSJ-1A strain.

1. WSJ-IA Culture Morphology and Physiological and Biochemical Characteristics

(1) Culture Characteristics

Aerial mycelium, substrate mycelium and the color of the soluble pigment of the strain cultured in different medium were observed, the results are shown in Table 1.

(2) Microscopic Characteristics

Fibrillae of spores were soft and winding, hook-like and spiral; spores cylindrical and oval.

TABLE 1 Culture morphology of WSJ-IA strain Culture Substrate Soluble characteristics Aerial mycelium mycelium pigment Czapek medium extremely few, lotus seed white not observed white Glucose asparagine extremely few, yellow-brown not observed medium off-white Glycerol asparagine no aerial lotus seed yellow not observed medium mycelium Inorganic salt starch no aerial light khaki not observed medium mycelium ISP-2 medium white earthy brown not observed Oat flour medium white Ivory yellow not observed Gause's No. 1 extremely few, light khaki not observed medium ivory-white Santa's medium no aerial Chestnut Brown not observed mycelium Note: Czapek medium: Cane sugar: 30 g, NaNO₃ 3.0 g, MgSO₄•7H₂O 0.5 g, KCl 0.5 g, FeSO₄•4H₂O, K₂HPO₄ 1.0 g, agar 15.0 g, distilled water1.0 L, pH 6.0-6.5. Glucose asparagine medium: Glucose 10 g, asparagine 0.5 g, K₂HPO₄ 0.5 g, agar 15.0 g, distilled water1.0 L, pH 7.2-7.4. Glycerol asparagine medium: Glycerol 10 g, asparagine 0.5 g, K₂HPO₄ 0.5 g, agar 15.0 g, distilled water1.0 L, pH 7.2-7.4. Inorganic salt starch medium: Soluble starch 10.0 g, MgSO₄•7H₂O 1.0 g, NaCl 1.0 g, (NH₄)₂SO₄ 2.0 g, CaCO₃ 2.0 g, K₂HPO₄ 1.0 g, MnCl₂•4H₂O 10 mg, FeSO₄ 10 mg, ZnSO₄•7H₂O 10 mg, agar 15.0 g, distilled water 1.0 L, pH 7.2. ISP-2 medium: Yeast extract 4.0 g, Malt extract 10.0 g, glucose 4.0 g, agar 20.0 g, distilled water 1.0 L, pH 7.2-7.4. Oat flour medium: Oat flour 20.0 g, Trace salt solution 1 mL, agar15 g, distilled water 1.0 L, pH 7.2, wherein: Trace salt solution: FeSO₄•7H₂O 0.1 g, MnCl₂•4H₂O 0.1 g, ZnSO₄ •7H₂O 0.1 g, 100 mL distilled water. Gause's No. 1 medium: Soluble starch 20.0 g, KNO₃ 1.0 g, K₂HPO₄ 0.5 g, MgSO₄•7H₂O 0.5 g, NaCl 0.5 g, FeSO₄•7H₂O 0.01 g agar 15.0 g, distilled water 1.0 L, pH 7.2-7.4. Santa's medium: KH₂PO₄ 0.5 g, MgSO₄•7H₂O 0.5 g, citric acid 2.0 g, Ferric ammonium citrate 0.05 g, glycerol 60 mL, Asparagine 4.0 g, agar 15.0 g, distilled water 1.0 L, pH 7.4.

(3) Physiological and Biochemical Characteristics

A. Detection the utilization of a carbon source by the WSJ-IA strain in the basal media selected.

Basal medium: (NH₄)₂SO₄ 2.0 g, MgSO₄.7H₂O 0.2 g, NaH₂PO₄.H₂O 0.5 g, CaCl₂.2H₂O 0.1 g, K₂HPO₄ 0.5 g, distilled water 1.0 L. Add 0.1%-0.5% of the carbon source to be measured into the basal medium. After sterilization, inoculate the medium with bacterial suspension, culture at 28° C., transplant for three generations successively. Determine utilization of the WSJ-IA strain on the carbon source according to the status of cell growth.

B. Basal medium measurement of malonic acid utilization: Basal medium: Yeast extract 1.0 g, (NH₄)₂SO₄ 2.0 g, K₂HPO₄ 0.6 g, KH₂PO₄ 0.4g NaCl 2.0 g, sodium malonate 3.0 g, bromothymol blue 0.025 g, distilled water 1.0 L, pH 7.0-7.4. After sterilization, inoculate the medium with bacterial suspension, culture at 28° C. for 1-2 days, malonic acid utilization by the bacteria is indicated when the medium turns its color from green to blue.

C. Basal medium measurement of tartaric acid utilization: Basal medium: peptone 10.0 g, NaCl 5.0 g, sodium tartrate 10.0 g, bromothymol blue (0.2%) 12.5 mL, distilled water 1.0 L, sterilize the medium before use. Prepare the saturated solution of lead acetate simultaneously. Inoculate the medium with bacterial suspension, culture at 28° C. for 14 days. Add isometric lead acetate solution, utilization of tartaric acid by the bacteria is indicated when the color of the medium turns green yellow with small amount of lead acetate precipitation.

D. liquefaction of gelatin: Basal medium: peptone 5.0 g, gelatin 100-150 g, distilled water 1.0 L, pH 7.2-7.4, and sterilized. After culture of the bacteria for 18-24 hours, puncture inoculate the suspension into gelatin medium, at the same time set the non-inoculated control. Culture the samples at 20° C. in an incubator for 2, 7, 10, 14 and 30 days, observe the cell growth and gelatin liquefaction at room temperature low than 20° C. If the results show the growth of bacteria, and that no depression of the gelatin surface is observed and the gelatin clot is stable, these means gelatin liquefaction negative.

E. Milk reaction: Boil fresh milk and place it in the refrigerator overnight. Take underlying skimmed milk, add 4 ml of a 2.5% litmus aqueous solution (2.5 g litmus immersed in 100 ml distilled water overnight, filtered subsequently), into 100 ml skimmed milk, add the mixture into test tubes to heights of about 4 cm, respectively. Sterilize the test tubes and inoculate with the strain, culture at 28° C. for 1, 3, 5, 7, 14 and 30 days. The results show that milk peptonized into cakes.

F, Reductin of nitrates: Nutrient agar medium 1.0 liters, KNO₃ 1.0 g, pH 7.0-7.6, Dispense 4-5 mL above medium into each of the test tubes, then sterilize. Griess reagents: a) dissolve 0.5 g sulfanilic acid in 150 ml dilute acetic acid (10%); b) dissolve 0.1 g-naphthyl amine in 20 ml distilled water and 150 ml dilute acetic acid (10%). Diphenylamine reagent: dissolve 0.5 g diphenylamine in 100 ml concentrated sulfuric acid, dilute with 20 ml distilled water. Inoculate the strain into nitrate medium, culture at 28° C. for 1, 3, 5 days, add small amount of the 1-, 3-, 5-day culture in clean tubes, add in a drop of a) and b) reagents, respectively, the color of the solution turns red demonstrated the reduction of nitrate to nitrite; add in a drop of diphenylamine reagent, no blue reaction can be observed.

G. Tyrosinase test: Inoculate the strain in Gause's No. 1 liquid medium at 28° C. for 7, 9, 12 days, respectively, sample 2 ml culture broth, centrifuged and fetch the supernatant, add in 2 mL phosphate buffer (pH 5.9) and 1 ml 0.04% tyrosine solution, keep the temperature at 37° C., incubated for 5 minutes, no red reaction is observed.

H. Amylase test: Inoculate the strain into BPA medium, with 0.2% soluble starch agar, culture for 2-5 days at 28° C. After obvious colonies are formed in agar plates, drop iodine solution (iodine 1.0 g KI 2.0 g, 300 mL distilled water) on the plate. Formation of transparent circle around colonies with no change of color indicates hydrolysis of starch.

The physiological and biochemical characteristics of the strain WSJ-IA is shown in Tab. 2.

2. The analysis on molecular systematic characteristics of WSJ-IA

(1) 16 S rDNA gene sequence:

16 SrDNA is a part of the bacterial ribosome, it is the DNA sequence in the chromosome of a bacterium, which is responsible for encoding rRNA. Because it is highly conserved in genetics, its sequence has been generally recognized as one of the characteristics of bacterial molecular taxonomy.

Following 16 SrDNA promers are used: 5′-AGAGTTTGATCMTGGCTCAG-3′, 5′-GGTTACCTTGTTACGACTT-3′.

Use the total DNA of bacterial strain WSJ-IA as template carry out PCR, the procedures are: 96° C. predenaturation for 1 min; in each of the 25 cycles, denature at 96° C. for 30 s, anneal at 50° C. for 30 s, extend at 72° C. for L5 min; subsequently, extend at 72° C. for 10 min to obtain the 1393 by sequence, see Tab. 1.

TABLE 2 Physiological and biochemical characteristics of the strain WSJ-IA Result characteristics Utilization of carbon source glucose + mannose + mannitol − lactose − galactose + sorbose − sorbierite − maltose + saccharose −− melibiose − melezitose − rhamnose − raffinose − trehalose + fructose − xylose − ribose − synanthrin − salicine + amygdalin − euonymol − erythritol − myoinosito − glycerol + starch + glycogen + sodium gluconate + sodium malate + sodium succinate + sodium malonate +w Sodium tartarate + Biochemical characteristics Liquefaction of − gelatin Milk reaction peptonized Reduction of + nitrate tyrosinase − Amylase + Note +: positive; −: negative; +w: weak positive

TABLE 3 Comparison of WSJ-IA 16S rDNA gene sequence with known bacteria Order homol- NBRC serial NCBI serial number Similar strain ogy % number number 1 Streptomyces 99.353 13039(T) AB184270 flavidovirens 2 Streptomyces 99.353 101003(T)  AB249953 albidochromogenes 3 Streptomyces 99.281 13382(T) AB184367 helvaticus 4 Streptomyces 99.281 NRRL B- AY999787 chryseus 12347(T)

Furthermore, this invention determined sequences of following five housekeeping genes commonly used in molecular taxonomy of Streptomyces, atpD gyrB, rpoB, recA and trpB in WSJ-IA strain. These are single-copied and protein encoding genes. They are structurally stable, there is no gap or stacking in these genes. Therefore, the sequencing results can be directly used to perform interspecific strain comparison on nucleotide- as well as the amino acid level, to further determine taxonomic status of WSJ-IA.

(2) Housekeeping Gene

A. atpD Gene Sequence

atpD gene is a subunit of the ATP synthase. It is highly stable and common in microbial species, hence it is suitable to be a molecular marker for the germline categorization. In this invention following primers are used

5′-GTCGGCGACTTCACCAAGGGCAAGGTGTTCAACACC-3′ 5′-GTGAACTGCTTGGCGACGTGGGTGTTCTGGGACAGGAA-3′

Use the total DNA of bacterial strain WSJ-IA as template carry out PCR, the procedures are: 96° C. predenaturation for 1 min; in each of the 28 cycles, denature at 96° C. for 30 s, anneal at 63° C. for 30 s, extend at 72° C. for 1.0 min; subsequently, extend at 72° C. for 10 min to obtain the 680 by sequence, see Tab. 2.

B. gyrB Gene Sequence

gyrB is a subunit of DNA gyrase tetramer, it belongs to prokaryotes type II DNA topoisomerase. It regulates DNA topology by its effects of cutting and religating DNA, it has some relationship with the resistance of some antibiotic producing bacterium strains, and has high degree of stability and universality in microbial species, as a result it is suitable for molecular mark of phylogenetic classification. Therefore, its sequence has been generally recognized as one of the characteristics of bacterial molecular taxonomy.

Following primers are used in this invention:

Use the total DNA of bacterial strain WSJ-IA as template carry out PCR, the procedures are: 96° C. predenaturation for 1 min; in each of the 28 cycles, denature at 96° C. for 30 s, anneal at 65° C. for 30s, extend at 72° C. for 1.5 min; subsequently, extend at 72° C. for 10 min to obtain the 1177 by sequence, see Tab. 3.

C. rpoB Gene Sequence

rpoB is a b-subunit of RNA polymerase, it is extensive present in Streptomyces.

Following primers are used in this invention:

5′-GAGCGCATGACCACCCAGGACGTCGAGGC-3′ 5′-CCTCGTAGTTGTGACCCTCCCACGGCATGA-3′

Use the total DNA of bacterial strain WSJ-IA as template, Carry out PCR, the procedures are: 96° C. predenaturation for 1 min; in each of the 28 cycles, denature at 96° C. for 30 s, anneal at 65° C. for 30 s, extend at 72° C. for 1.3 min; subsequently, extend at 72° C. for 10 min to obtain the 870 bp sequence, see Tab. 4.

D. RecA Gene Sequence

RecA is a recombinase, it plays an important role in the processes of DNA homologous recombination and repair of damaged DNA. The presence of RecA is a very important factor to ensure the stability of strain genomic DNA, therefore its sequence has been generally recognized as one of the characteristics of bacterial molecular taxonomy.

Following primers are used in this invention:

5′-CCGCRCTCGCACAGATTGAACGSCAATTC-3′ 5′-GCSAGGTCGGGGTTGTCCTTSAGGAAGTTGCG-3′

Use the total DNA of bacterial strain WSJ-IA as template, carry out PCR, the procedures are: 96° C. predenaturation for 1 min; in each of the 28 cycles, denature at 96° C. for 30 s, anneal at 60° C. for 30 s, extend at 72° C. for 1.0 min; subsequently, extend at 72° C. for 10 min to obtain the 701 bp sequence, see Tab. 5.

E. TrpB Gene Sequence:

trpB gene encodes tryptophan synthase which is involved in the primary metabolism of Streptomyces, this gene is considered to have strain species specificity, its sequence has been generally recognized as one of the characteristics of bacterial molecular taxonomy.

Following primers are used in this invention:

5′-GCGCGAGGACCTGAACCACACCGGCTCACACAAGATCAACA-3′ 5′-TCGATGGCCGGGATGATGCCCTCGGTGCGCGACAGCAGGC-3′

Use the total DNA of bacterial strain WSJ-IA as template, carry out PCR, the procedures are: 96° C. predenaturation for 1 min; in each of the 28 cycles, denature at 96° C. for 30 s, anneal at 66° C. for 30 s, extend at 72° C. for 1.0 min; subsequently, extend at 72° C. for 10 min to obtain the 611 bp sequence, see Tab. 6,

The results in Tabs. 3 and 4 show that there is no complete consistency between 16 SrDNA and five housekeeping gene sequences of the bacterial strain WSJ-IA, and gene sequences of known strains, so it can be decided that WSJ-IA might be a new species of Streptomyces.

TABLE 4 Comparisons of the housekeeping gene sequences of WSJ-IA with known bacteria homology % Gene bank serial number Similar strains Amino Amino gene nucleotides Amino acids nucleotides acids nucleotides acids atpD S. griseus S. griseus 96 99 AP009493 YP0018236 subsp. griseus subsp. griseus 75C13350 NBRC13350 NBRC13350 gyrB S. spiroverticillatus S. spiroverticillatus 93 94 AB014337 AB072882 rpoB S. avermitilis S. avermitilis 94 93 BA000030 NP_826091 MA-4680 MA-4680 recA S. avermitilis S. avermitilis 91 95 BA000030 NP_823668 MA-4680 MA-4680 trpB S. griseus S. flavogriseus 92 99 AP009493 ZP_05806307 subsp. griseus ATCC 33331 NBRC13350 Note: S: Streptomyces

Example 3 Determination of Pilot-scale Fermentation Titer of WSJ-IA Bacteria Strain

WSJ-IA strain was cultured in the slant medium described in Example 2 at 28° C. for 7-10 days, a piece of above culture was scooped to inoculate onto the seed medium (soybean cake flour 1.5%, starch 3.0%, NaCl 0.4%, CaCO₃ 0.5%, fish peptone 0.3%, KH₂PO₄ 0.05%), cultured at 28° C. for 48 hours in the stage A, subsequently transferred to stage B to culture at 28° C. for 24 hours, then transferred to 50 L seed tank, cultured for 36 hours, and subsequently transferred into a 2 ton fermentation tank to culture in seed medium (Culture medium: glucose 0.5%, starch 6.0%, yeast powder 0.5%, fishmeal 2.0%, NH₄NO₃ 0.6%, NaCl 1.0%, CaCO₃ 0.5%, KH₂PO₄ 0.05%, MgSO₄ 0.1%), fermentation was carried out at 28° C. to culture for 96 h. The supernatant of fermentation broth was sampled, diluted with pH 7.8˜8.0 phosphate buffer containing 3% NaCl. Bacillus [CGMCC(B)63501] was used as test bacterium to determine the fermentation titer using the standard curve method in accordance with the Chinese Pharmacopoeia 2010 ed. II, Appendix XI in following medium: polypeptone 0.6%, beef extract powder 0.15%, yeast extract paste 0.6%, glucose 0.2%, agar 1.5-2.0%, with acetyl spiramycin as control. The experiment was repeated three times to obtain an average WSJ-IA fermentation titer of 1160 μg/ml, in comparison, fermentation with WSJ-2 strain containing ist single gene gave rise to an average titer of 280 μg/m1 (Tab. 5).

Example 4 Yield Determination of the Product of Isovaleryl Spiramycin I Component Fermenting with WSJ-IA Strain

The fermentation broth obtained in Example 3 was sampled, pH of the broth adjusted to 8.5, it was extracted with an equal volume of ethyl acetate, and the ethyl acetate extract concentrated to dryness, dissolved in methanol. The solution was separated using a Kromasil C18 column (4.5 mm×150 mm, 5 μm); mobile phase: methanol: sodium dihydrogen phosphate solution (53:47 v/v); detection wavelength: 231 nm; flow rate: 1.0 mL·min⁻¹; column temperature 25° C.; sample size: 10-20 μL. Contents of isovaleryl spiramycin I component in the broth was calculated using the HPLC results (FIG. 3). The results from 3 experiments showed that, fermenting with WSJ-IA strain and. WSJ-2 strain containing ist monogene, the average total content of isovaleryl spiramycin I component was 12.061% and 7.088%, respectively. After fermentation in accordance with Example 3, the fermentation titers of the two strains were measured with microbiological assay, and the products were analyzed using HPLC (FIG. 3). According to the HPLC peak areas obtained, isovaleryl spiramycin I component produced with the two strains were compared, the ratio of isovaleryl spiramycin I vs. spiramycin produced with the two strains, respectively, calculated. The results showed that introduction of ist-acyB2 gene increased the fermentation titer of the WSJ-IA by 414%, the produced isovaleryl spiramycin I content was increased by 170.2%, meanwhile, the production of spiramycin was decreased accordingly. This increased the ratio between isovaleryl spiramycin I content and spiramycin content by 218% (Tab. 5).

This invention provides a strain capable of producing isovaleryl spiramycin I containing ist-acyB2 gene, under a certain fermentation condition, This strain increases the production of isovaleryl spiramycin I by a factor of 1.7, and increases the fermentation titer by a factor of 4.14 in comparison with the strain containing only ist gene.

TABLE 5 Comparison of the fermentation titer using WSJ-IA and WSJ-2 strains and component contents fermentation Isovaleryl Isovaleryl titer Spiramycin spiramycin I spiramycin I/ Strains (μg/mL) peak area (%) peak area(%) spiramycin(%) WSJ-2 1. 260  1. 61.146 1. 6.980  1. 11.42 2. 280  2. 63.756 2. 7.150  2. 11.21 3. 300  3. 62.223 3. 7.134  3. 11.47 average 280 average 62.375 average 7.088 average 11.36 WSJ-IA 1. 1040 1. 47.825 1. 10.956 1. 22.91 2. 1250 2. 48.982 2. 13.013 2. 26.57 3. 1190 3. 49.527 3. 12.214 3. 24.66 average 1160 average 48.778 average 12.061 average 24.72 

1. A strain of genetically engineered bacterium producing high content of isovaleryl spiramycin I component with high productivity, wherein said genetically engineered bacterium is a clonal strain with isovaleryl transferase gene ist and the acyB2 regulatory gene linked with it co-expressed in isovaleryl spiramycin I producing bacterium WSJ-2.
 2. A method for constructing the strain of genetically engineered bacterium according to claim 1, the method comprising: A) using total DNA of the heat-resistant Streptomyces (Streptomyces thermotolarences CGMCC4.1501) as a template, to design primers according to ist-acyB2 sequence announced by NCBI, carrying out PCR to obtain ist-acyB2 linked gene segment, inserting appropriate cleavage sites; or also, ligating ist and acyB2 gene fragments, respectively, with the integrative vector transferrable to the isovaleryl spiramycin I producing bacterium strain, to obtain recombinant plasmid containing ist-acyB2 gene; and B) transferring the recombinant plasmid containing ist-acyB2 into isovaleryl spiramycinl producing bacterium WSJ-2 by means of resistance screening to obtain transformant, after continuous passage under non-dosing conditions and testing with dosing to obtain stable expression of isovaleryl spiramycin I producing bacterium containing recombinant plasmid, and constructing a strain being named WSJ-IA, culture Collection No. CGMCC No.3942.
 3. The method according to 2, wherein the WSJ-IA stain obtained is validated to contain ist-acyB2 sequence on gene level by means of PCR.
 4. The method according to 2, wherein the constructed WSJ-IA strain, after culture and fermentation, results in a fermentation titer of not less than 1160 μg/mL, the total production of isovaleryl spiramycin I not lower than 12.061%. 